Booleans

Originally published on php2rust.dev — part of the PHP to Rust course. View this lesson on the original site.

Both Rust and PHP have a boolean type. The main difference is how strict the type system is and how other values convert to boolean.

Rust

fn main() {
    let is_rust_fun: bool = true;
    let is_compiled: bool = false;

    if is_rust_fun {
        println!("Rust is fun!");
    }

    // Logical operators
    let a = true && false;   // false
    let b = true || false;   // true
    let c = !true;           // false

    println!(
        "is_rust_fun={}, is_compiled={}, a={}, b={}, c={}",
        is_rust_fun, is_compiled, a, b, c
    );

    // No implicit conversion: this would not compile
    // if 1 { }   // Error: expected bool, found integer
}

Rust's bool is a distinct type. Integers and other types do not implicitly convert to bool.

PHP

<?php
$is_rust_fun = true;
$is_compiled = false;

if ($is_rust_fun) {
    echo "Rust is fun!\n";
}

$a = true && false;   // false
$b = true || false;   // true
$c = !true;           // false

// PHP allows many values as "truthy" or "falsy"
if (1) { }        // Truthy
if (0) { }        // Falsy
if ("") { }       // Falsy
if ("hello") { }  // Truthy
if ([]) { }       // Falsy (empty array)

PHP treats many values as truthy or falsy when used in a boolean context.

Comparison

• Rust: bool only; no implicit conversion from numbers or strings.
• PHP: bool plus truthy/falsy rules for other types in boolean context.

In Rust you must use explicit comparisons (e.g. if x != 0) instead of relying on truthiness.

References

• Rust: Boolean Type
• Rust: bool
• PHP: Booleans
• PHP: Type Juggling

What's next

Next: Characters.

From PHP to Rust — Rust Syntax and Functions